Safety-plug.



.' No. 848,206. PATENTED MAR. 26, 1907.

B. W. ROBINSON. SAFETY PLUG.

APPLICATION FILED JAN. '7, 190 7.

A 7 a e 1 :buvem orJ below a predetermined point.

UNITED STATES PATENT clarion.

BLISS W. ROBINSON, OF BOSTON, MASSACHUSETTS.

SAFETY-PLUG.

drawing, is a specification, like letters on the (lrawing'representing like parts. Y

This invention relates to safety-plugs, such as are used in steam-boilers for givingiindicationwhen the water-level in the boiler gets These safetyplugs as commonly made are in the form of a bushing which is screwed. into the flue-sheet, fire-sheet, or some other suitable portion of the boiler at the desired point, said plugs being filled withsome fusible metal. Usually the inner ends of these plugs extend into the water-space of the boiler, so that they are surrounded by water, and so long as the waterlevel is above the plugs the water keeps the fusible metal therein sufiiciently cool so that it will not melt. These plugs, however, often become so rusted into the fire-sheet that it is almost impossible to remove them when they become damaged without injuring the firesheet or breaking the shell of the plug; and it is one of the objects of my present invention to provide a novel form of plug in which the shellor casing inclosingthe fusible metal is" made in a separate piece from the bushingthat screws into the fire-sheet, so that to renew the plug .it is not necessary to remove the bushing, but simply to remove the shell or holder from the bushing and insert a new shell or holder.

In safety-plugs as commonly employed, too, the fusible metal extends into that portion of the plug which is screwed into the fire-sheet, and as a result the water surrounds only a portion of the fusible metal. With this type of plug it often happens that the severe heat to which the fire-sheet is subjected softens the fusible metal sufficiently so that it will begin to flow even though the inner end of the plug is surrounded by water, in which case the plug might blow before the water-level reached the danger-point. To avoid this objection, I have in the present embodiment of my'invention so designed my plug that the water surrounds the entire portion of .the shell or holder in which the fusible metal is situated,.

so that the heat cannot be conducted to the fusible metal through the fire-sheet in suffi- Specification of Letters Patent. I

Application filed Januar 7,1907. Serial No.-851,084.

Patented March 26, 1907.

cient quantities to melt said metal so long as the water is above the level of the plug.

Another feature of mylinvention relates to a novel way of anchoring the fusible metal in the shell.

A construction embod gmyinvention will now be described, an the invention will then be pointed out in the appended claims.

Referring to the drawings, Figure 1 shows one end of a boiler, showing my improved safety-plug. Fig. 2 is alongitudinal section through the safety-plug on the line m as, Fig. 3. Fig. 3 is an end view.

I have shown in Fig. 1 at 3 a tubular boiler of any usual construction, 4 being the fire-sheet into which the flues orfire-tubes 5 are secured as usual.

My improved safety-plug is screwed into the fire-sheet 4 at the desired point, which is below the normal water-level and below the dangerpoint. with a screw-threaded portion 9, which is The safety-plug is formed screw-threaded into the fire-sheet 4, and is also provided with a shell or holder 7 in which the fusible metal 8 is located. The

shell or holder 7 is tubular in shape, and the fusible metal 8 extends forwardly therein to a point 10 nearly to the fronte'nd'thereof, In order to prevent the fusible metal from be ing softened sufficiently so that it will flow by conduction of heat thereto through the fire-sheet while the inner end of the plug is still covered with water, I form in the plug an annular chamber 11, which surrounds the shell 7 and extends as far toward the front of the plug as the fusible metal does, so that when the plug is in place there will be a body of water surrounding the portion of the shell 7 that is filled by the fusible metal 8. So long as the plug is covered with water the entire body of fusible metal will be kept sufiiclentl y cool so that it will not flow and the, lug Wlll remain intact until the water-leve in the boiler drops below the plug. .1 have also in this embodiment of my invention shown the fusible metal S as anchored in the shell by providin said shell with apertures 12, which become filled with anchor portions 13 of fusi ble material when the plug-is filled. These anchor portions serve to more securely hold, the fusible material in the shell and also assist materially in keeping the fusible metal '3, at the same temperature as the water in theboiler. I r

In order to facilitate the renewal of the plug when it becomes damaged, I prefer .to make the shell 7 independent and separate from the screw-threaded bushing member 9,:

so that the shell may be removed from the bushing without removing the bushing from the fire-sheet. As herein shown, the member 9 has a head 14, provided with a bore of smaller diameter than the annular chamber 11,said bore being enlarged at its outer the bushing. The shell 7 is preferablysuitably formed at its outer end so that a wrench may be applied thereto for unscrewing it from the bushing 9, and in the preferred emzo hodiment of my invention this is accom-v plished by providing the end with the square wrench-socket 20. In practice the bushing 9 becomes so rusted into the fire-sheet that it is almost impossible to remove it; but bv placing fusible metal 8 in the shell 7, which is separate from the bushing and removably supported thereby, the portion of the plug containing the fusible metal .may be readily removed after the plug blows and a new por- 0 tion inserted without disturbing the bushing the fi heet.

I desire to call attention to the fact that the seat or shoulder 18 is located between the screw-threads on the head 17 and the portion- 5 of the shell 7 that projects into the water.

In inserting a plug thisseat 18 will be so madev that a water-tight joint will be formed, and thus the water is prevented from workiug its wayinto the screw-threads 16. With o. this construction, therefore, the screwthreaded head 17 of the shell will never become so rusted to the bushing 14 as to prevent the shell from being removed. This placing of the seat between the screw- 5 threaded portion of the shell and the portion projecting into the water is one of the important features of the invention in a con- 'struction wherein the shell is made removable, from the bushing. It is not essential to my invention, however, that the shell portion 7 should be made separate from the bus ing portion 9, as the two might be made integral, although I refer ,to make them separate, for reasons a ove stated.

5 5; Ihelieve I am the first to invent a safetyplug which is formed'with an annular waterchamber, such as 1 1, that extends into the ph as far toward the front thereof as the fusi l e materiaL-so that When in place the 6p fusible material is surrounded'on all sides,-

witha body of waterfand *I desire to claim 4 this feature broadly, whether the plug be.

' formed two partsv orin one. I also be? lieve that I am the ffirst to provide a lug '65 having a bushing to screw into-.the fire-s; eet

shoul and a separate detachable shell or holder for holding the fusible material. I also believe that I am the first to provide a safety-plug which is made in two )arts with the seat, such as 18, situated etween the screw- 7o threaded head of the shell and the-portion which pro'ects into the water.

It will e understood, of course, that the shell 7 may be made of any length desired, according to the location in which the plug is 7 5 Having fully described my invention, what I claim as new, and desire to secure by Let ters Patent, is

1. A'safety-plug for boilers provided with a chamber containing fusible material and, another chamber constituting a water-space surrounding the first-named chamber.

2. A safetylug provided with an exterior screw-thread portion for screwing .intoaflue-sheet of a boiler, and a shell portion'extending therethrough and containin fusible I material, said screw-threaded portion and shell portion being spaced from each other.

3. -A safety-plug having an annular screwthreaded bushing portion and a shell portion concentric therewith and extendin therethrough but spaced therefrom, an fusible mater al within the'shell portion.

4. A safety-plug comprising a" bushing 5 adapted to be screw-threaded mto a fluesheet, and a shell ortion containing fusible material removab y carried by the bushin portion and removable from the outer en therecg. f 1 Y 5. sa et ,u com risin a bushin adapted to lg; cre w-thre ded nto a flue sheet, and a shell portion containingfusible material screw-threaded to the bushing portion and removable from the outer end :05 thereof.

6. A safetyplug comprising a bushing adapted to be screw-three, ed to a flue-sheet, a shell portion screw-threaded to the bushin portion 'and exposed through said perfora-- tions.

8. Asafety-plu com rising ashell,'fusib1e material within t e she l, and means to anno chor said fusible material tofthe shell by the material itself. a

9. A safetylug comprising a bushing portion provide with interior screw threads and a seat, and" a shell portion extending 1-25 through'the bushing portion and having a er to engage said seat, and exteriorscrew-threads to en age the interior screwthreads of the bushing, said seat being situated between the screw-threaded portion of 1 0 the shell and the portion projeeting' into the 1' in and shell at a point between the screwwater.

10. A safety-plug comprising a bushing portion having interior screw-threads at its 5 outer end, and a shell portion to contain fusible metal extending through the bushing portion and provided With an exteriorlyscrew-threaded end to engage the interior screw-threads of the bushing, and means to 10 make a water-tight joint between thehushthreaded portion of the shell and the inner end thereof.

In testimony whereof I have signed my name to this specification in two subscribing witnesses.

BLISS W. ROBINSON.

Witnesses:

LOUIS C.SM1T11, BERTHA F. HEUSER.

the presence of 15 

